Atomic radius down group 2
After studying this page, you should be able to:
- describe and explain the trend in atomic radius down group 2
The table shows atomic radius values for the common elements in group 2 (the alkaline earth metals).
|Element||Symbol||Atomic number||Atomic radius /nm|
Atomic radius is the distance from the centre of the nucleus to the edge of the surrounding electron cloud. It is measured or calculated in different ways, so values vary from source to source.
Description of trend
The graph shows how atomic radius varies down group 2:
- as the atomic number increases, the atomic radius increases.
Explanation of this trend
Going down group 2:
- there are more filled shells between the nucleus and the outer electrons …
- the outer electrons are more shielded from the attraction of the nucleus …
- so the electrons in the higher energy levels are further from the nucleus …
- the atomic radius increases.
You might expect the atomic radius to decrease because the nuclear charge increases going down the group. However, this does not happen: although the electrons in the inner shells become closer to the nucleus, the factors described in the Explanation have a greater influence overall.